This invention relates to a solid state image pickup device and in particular an image pickup device suitable for narrow band transmission which uses a charge transfer device.
In a video telephone, for example, a slow scan type image pickup tube and image pickable storage tube are used in an image pickup device to transmit in narrow band width a picture image which is obtained in a standard television system. Since, however, the image pickup tube and storage tube are constructed of vacuum tubes the associated device is made bulky and requires electric power of a heater. Furthermore, they are unstable and disadvantageous from the standpoint of reliability as well as a life service.
To improve such disadvantages a solid state image pickup device 10 in FIG. 1 is considered comprising an imaging section 11, storage section 12 and readout section 13 using a charge transfer element. In this image pickup device 10 an electric charge corresponding to a quantity of light of a projected optical image is produced for a required imaging time t in a standard television system a time corresponding to substantially one frame time (1/30 second) in the imaging section. The electric charge is transferred to the storage section 12 where a line of electric charge is positioned, and each line of electric charge is transferred from the right end of the storage section 12 to the readout section 13 and outputted as a video signal from an output electrode in the readout section. Such a readout operation is sequentially repeated, thus completing the transfer of a one frame picture image consisting of electric charge transferred from the storage section 12.
When the electric charge stored in the storage section 12 begins to be read out as a video signal from the readout section 13, an electric charge corresponding to the next frame begins to be created in the imaging section 11. In consequence, the imaging time must coincide with the readout time in which all the electric charge stored in the storage section is read out as a video signal. That is, this time must coincide with a one frame time (1/30 second) in the standard TV system. However, the readout operation should be effected at low speed to transmit a picture image in narrow band width. In this case there is required a long readout time of about 1 to 10 seconds. In the conventional charge transfer element it is impossible to retain electric charge in the storage section for such a long time. If an imaging operation is effected over a long time, it is impossible to provide a practical device, since a moving subject prominently impairs a picture image quality due to the overlap of picture images.
In a solid state image pickup device using a charge coupled device, as disclosed and claimed in U.S. Pat. No. 3,777,061, desired optical information is obtained by distributing an electric charge on an imaging section to the left and right of a storage section. However, this device can not be applied to narrow band transmission, because the imaging time coincides with the readout time and an electric charge created at the imaging section can not be stored for a long time.